In the related art, a magnetic core formed of a soft magnetic material such as soft ferrite, an amorphous soft magnetic alloy, a permalloy, and a nanocrystalline soft magnetic alloy, which exhibit properties of high permeability and low magnetic core loss, has been used for various magnetic components such as a current transformer, a noise suppression component, a high frequency transformer, a choke coil, and a core for accelerator.
For example, the soft ferrite is excellent in high frequency properties, but has a low saturation magnetic flux density Bs, and is inferior in temperature properties, and thus is easily magnetically saturated. Particularly, in a case where the soft ferrite is used for components of a high current circuit such as a current transformer or a choke coil having a possibility of DC superimposition, there are problems in that satisfactory properties cannot be obtained, the size of a component becomes larger, the magnetic properties with respect to the temperature are greatly changes, and the components are inferior in the temperature properties. In addition, an Fe-based amorphous alloy representing Fe—Si—B based alloys has problems in that a B—H curve having good linearity is not exhibited even with heat treatment performed in magnetic field, and that in a case of being excited at audio frequency to be used, the noise of components is large. Further, a Co-based amorphous alloy has the following problems. That is, the Co-based amorphous alloy has a low saturation magnetic flux density of 1 T or less, and thus the size of the component becomes larger. In addition, the Co-based amorphous alloy is thermally unstable, and thus the change over time is large at the time of temperature rise. Furthermore, the raw materials of the Co-based amorphous ally are expensive.
It has been known that an Fe-based nanocrystal alloy ribbon exhibiting more excellent soft magnetic properties than those of the above-described soft magnetic materials is suitable for a magnetic core material for pulse power application such as an earth leakage breaker, a current sensor, a current transformer, a common mode choke coil, a high frequency transformer, and an accelerator. As a representative compositional system of the Fe-based nanocrystal alloy ribbon, Fe—Cu—(Nb, Ti, Zr, Hf, Mo, W, Ta)—Si—B-based alloys and Fe—Cu—(Nb, Ti, Zr, Hf, Mo, W, Ta)—B-based alloys have been known (refer to PTLs 1 and 2).
These Fe-based nanocrystal alloy ribbons are typically produced by a method of quenching from a liquid phase to produce an amorphous alloy ribbon, processing the amorphous alloy ribbon in a magnetic core shape as necessary, and then performing microcrystallization by heat treatment. As the method of quenching from a liquid phase to produce an alloy ribbon, a single roll method, a double roll method, a centrifugal quenching method, and the like are known, and in a case of mass production of super rapidly quenched alloy ribbons, the single roll method is mainly used. The Fe-based nanocrystal alloy is obtained by performing the microcrystallization on the amorphous alloy produced by the above-described method, and it has been known that the alloy exhibits a high saturation magnetic flux density and excellent soft magnetic properties which are equivalent to the Fe-based amorphous alloy, is less likely to change over time as compared with the amorphous alloy, and is excellent in the temperature properties.
In addition, an Fe-based nanocrystal alloy ribbon of Fe—Si—B—Cu-based or Fe—Si—B—P—Cu-based alloys, which exhibits high magnetic flux density, so as to respond to the recent demand for high energy density has been known (PTLs 3 and 4).
In recent years, a material exhibiting a B—H curve which is excellent in constant permeability having slightly low permeability such that a material is not magnetically saturated has been used as a highly-demanded magnetic core material such as a choke coil which is used in a DC superimposition state or an asymmetric AC excitation state, and a current transformer (CT) in which an AC current having an asymmetric waveform such as a half sine alternating current flows into a coil. In such applications, a material having the constant permeability of 6000 or less is typically used; however, a material exhibiting the constant permeability approximately in a range of 1000 to 3000 has been used in a case of being used as a current transformer (CT) which is suitable for detection for an AC current having an asymmetric waveform such as a sinusoidal alternating current, or detection for an AC current on which a DC current is superimposed. Particularly, in accordance with the requirement of accurate measurement of an asymmetrical current waveform or a distorted current waveform (asymmetric current waveform), a magnetic material capable of accurately measuring electric energy from the asymmetric current waveform has been demanded. It has been reported that as a magnetic material satisfying such a requirement, a material which exhibits a low residual magnetic flux density, low hysteresis, and good linearity of B—H curve is used, and a magnetic core (iron core) formed of an Fe-based soft magnetic alloy ribbon containing Co or Ni in which the heat treatment in the magnetic field is performed exhibits suitable properties as the aforementioned material (PTL 5, 6, and 7).